1. Field of the Invention
Embodiments of the present invention generally relate to downhole well tools. Particularly, aspects of the present invention relate to downhole flow valves. More particularly still, aspects of the present invention relate to downhole flow valves used to control the flow of fluid therethrough.
2. Description of the Related Art
Advancements in the oil and gas industry have allowed hydrocarbons in multiple zones of interest to be produced from a single well. One such development is the drilling of multilateral wells, in which a number of lateral wells are drilled from a primary wellbore. In such wells, each wellbore may pass through various hydrocarbon bearing zones or may extend through a single zone for a long distance. Additionally, production may be increased by perforating a wellbore in a number of different locations, either in the same hydrocarbon bearing zone or in different hydrocarbon bearing zones, and thereby increase the flow of hydrocarbons into the well.
One problem associated with producing from a well in this manner relates to the control of the flow of fluids from multiple zones of interest to and from the well. For example, in a well producing from a number of separate zones, or lateral branches in a multilateral well, one zone may have a higher pressure than another zone. As a result, the higher pressure zone may produce into the lower pressure zone rather than to the surface.
Production fluids from one zone may be kept separate from the production fluids of another zone by zonal isolation. Zonal isolation typically involves inserting a production tubing into the well, isolating each of the perforations or lateral branches with packers, and controlling the flow of fluids into or through the tubing. Previous flow control systems typically only provide for either on or off flow control. More recently, flow control systems include a flow throttling feature to further alleviate the aforementioned problems.
Sliding sleeves are commonly employed in pipe strings to open and close access openings in the tubing as well as throttle the flow of fluid through the tubing. An example of a prior art sliding sleeve system is shown in U.S. Pat. No. 5,263,683. The patent discloses an internal sliding sleeve within a ported pipe section. Shifting the sleeve axially so that openings in the sleeve align with openings in the pipe establishes a flow path through the wall of the pipe section. The seals above and below the pipe ports remain covered and protected by the sliding sleeve in both the open and closed positions. In this prior art device, the flow path for fluids entering or leaving the pipe extends through the pipe ports as well as the sleeve openings. However, the surface contours of the pipe ports and the sliding sleeve openings, as well as the annular space between the sleeve and the internal pipe wall, induce turbulent flow as the fluids traverse the flow path. The turbulent flow, in turn, when combined with entrained abrasives such as sand can quickly wear away and otherwise damage the pipe and sliding sleeve assembly.
Additionally, the design of the sliding sleeve may also lead to turbulent flow in the annular space between the pipe and the casing. The turbulent flow may increase wear on the casing or the pipe, thereby decreasing their burst, collapse, and tensile capabilities. Moreover, the pipe ports are oriented radially on the pipe section, which further decreases the tensile strength of the pipe section.
There is a need, therefore, for a choke valve assembly for controlling the flow of fluid through a tubing which decreases the wear on the choke valve assembly and the surrounding wellbore. There is a further need for a choke valve assembly that reduces the turburlent flow surrounding the ports of the choke valve assembly. There is yet a further need for a method of throttling the flow of fluid through the choke valve assembly without decreasing the tensile strength of the choke valve assembly.